Ethernet is the preferred protocol for many types of networks because it is flexible, decentralized, and scalable. Ethernet comprises a family of frame-based computer networking technologies for local area networks (LANs), and defines a number of wiring and signaling standards for the Physical Layer of the Open Systems Interconnection (OSI) networking model and a common addressing format and Media Access Control (MAC) at the Data Link Layer. Ethernet is flexible in that it allows variable-sized data packets to be transported across different types of mediums using various nodes each having different transmission speeds.
Synchronous Optical Networking (SONET)/Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fibers or electrical interfaces. Due to SONET/SDH protocol neutrality and transport-oriented features, SONET/SDH is used for transporting substantially large amounts of telephone calls and data traffic over the same fiber or wire without synchronization problems. SONET/SDH network transmission standards are based on time-division multiplexing (TDM). TDM is a technology where two or more signals or bit streams are apparently transferred simultaneously as sub-channels in one communication channel but physically take turns on the channel. This is achieved by dividing the time domain into a plurality of recurrent timeslots, e.g. of about same length, one for each sub-channel. As such, one TDM frame corresponds to one timeslot per sub-channel. In networks that use SONET/SDH and/or TDM, such as some Ethernet networks, the nodes synchronize their transmissions by exchanging a plurality of time references or time stamps.